Wednesday, January 28, 2009

FEMA flood plain maps for Arizona don't meet all standards

Arizona is not part of the 21% of the nation that has flood plain maps that meet all of FEMA's data quality standards, even after a $1 billion national map modernization program. As a result, the National Research Council issued a report (Mapping the Zone: Improving Flood Map Accuracy) this week on what is needed to improve flood map accuracy for protecting lives and property.

The study concluded that "map accuracy would be increased by updating and generating information using high-accuracy topographic data, such as that generated by "lidar," which measures elevation using aircraft-mounted lasers."

Just as importantly, the study focused on what information is needed to adequately convey risk. They state that "the maps and products must show where the flood hazard areas are located and the likely consequences of flooding, such as damage to houses or coastal erosion. Additionally, floodplain residents should know how their land elevation level compares with various possible flood heights, which will offer a finer discrimination of potential risk. Currently, maps that show only floodplain boundaries imply that every building in a designated flood zone may flood and every building outside the zone is safe."

[right, data quality standards projected to be achieved for individual counties by the end of the Map Modernization Program. Green counties meet or exceed national flood hazard data quality thresholds. Yellow counties meet some standards. In red counties, the maps have been updated digitally and a digital product has been issued. In beige counties, modernized maps have not yet been issued because the first phase of map production has not been completed or quality data do not exist. No study is planned in white counties because of funding shortfalls. Source: Paul Rooney, FEMA & NRC]

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